1. Field of the Invention
This invention relates to a method for controlling automatic transmission systems of the type including automatic power transmissions providing a plurality of gear reduction ratios, such as automatic mechanical transmissions, throttle controlled engines and coupling devices interposed the engine and transmission such as fluid couplings (i.e. torque convertors) and/or friction master clutches. In particular, the present invention relates to control system methods for vehicles with throttle controlled engines and automatic transmissions wherein gear selection and shift decisions are made and executed based upon measured and/or calculated parameters such as output shaft or vehicle speed, input shaft or engine speed, throttle position, and the like. More particularly, the present invention relates to automatic transmission control system methods of the type described above wherein digital microprocessor based electronic control units are utilized to control the system.
2. Description of the Prior Art
Automatic transmissions of both the automatic mechanical type utilizing positive clutches and of the planetary gear type utilizing frictional clutches are well known in the prior art, as are control systems therefor. Electronic control systems for automatic transmissions wherein gear selection and shift decisions are made based upon certain measured and/or calculated parameters such as vehicle speed, engine speed, rate of change of vehicle speed, rate of change of engine speed, throttle position, rate of change of throttle position, full depression of the throttle (i.e. "kickdown"), actuation of the braking mechanism, currently engaged gear ratio, and the like are known in the prior art. Examples of such automatic transmission control systems for vehicles may be seen by reference to U.S. Pat. Nos. 4,361,060; 4,073,203; 4,079,638; 4,140,031; 4,324,322; 4,253,348; 4,038,889; 4,226,295; 3,776,048; 4,208,929; 4,039,061; 3,974,720 and 3,942,393, the disclosures of which are all hereby incorporated by reference.
The prior art controls for automatic transmissions were usually electric or pneumatic analog devices and/or utilized a sequential or timing control philosophy whereby the individual operations and/or sub-operations required to perform a selected task were performed in accordance with a set sequence and/or set timing after the task was initiated and not on the basis of continuously updated command signals processed from current input signals.